We have recently established the procedures for the detection of cross-reacting antigens on tumor cells, fetal cells and sperm in strain A/J mice. This model system will enable us to characterize the antigens on syngeneic tumors and the host response to these antigens. The overall goal of the proposed research project is to evaluate the immunological reactions between tumor and host in terms of the nature of the cross-reacting antigen(s) between fetal, sperm and tumor cells, and in terms of the immune response of the host to these antigens. The specific aims of the project are: 1) to determine the biological and immunological characteristics of the cross-reacting antigen(s) on fetal, sperm and tumor cells; 2) To characterize the cell types involved in the immune responses of syngeneic hosts to these antigen(s); and, 3) To extend these studies to other tumor-host systems. These studies should enable a more comprehensive understanding of the immunological reactions between the tumor and the host, and will hopefully lead to more effective cancer therapy.